U.S. Pat. No. 4,946,838, assigned to E.R. Squibb & Sons, Inc., discloses a crystalline anhydrous form of the antibacterial agent, [3S-[3α(Z),4β]]-3-[[(2-amino-4-thiazolyl)[(1-carboxy-1-methylethoxy)imino]acetyl]amino]-4-methyl-2-oxo-1-azetidinesulfonic acid (Aztreonam). This crystalline, anhydrous form is designated as the β polymorph. According to the '838 patent, its main advantages compared to the α-polymorph are higher thermal stability, flowability and lower hygroscopicity. The new polymorph is characterized by X-ray powder diffraction.
Polymorph β can be obtained by crystallization of α-Aztreonam from anhydrous solvents such as alcohols, most preferably ethanol or by the precipitation of the Aztreonam salt with an organic amine in the presence of HCl. (see U.S. Pat. No. 4,826,973). U.S. Pat. No. 4,826,973, assigned to E. R. Squibb & Sons, Inc., discloses, in Table II, that the crystals of the β-form contain 0-1% water and 2.5% ethanol. This relatively high solvent content makes this form unsuitable for pharmaceutical formulations.